PERMANENT PREPARATIONS 407 



//. Tube Cultivations of Bacteria. When showing 

 typical appearances these may be preserved, if not 

 permanently, at least for many years, as museum 

 specimens, by the following method : 



1. Take a large glass jar 25 cm. high by 18 cm. diam- 

 eter, with a firm base and a broad flange, carefully 

 ground, around the mouth. The jar must be fitted 

 with a disc of plate glass ground on one 



side, to serve as a lid. 



2 . Smear a thick layer of resin ointment 

 (B.P.) on the flange around the mouth 

 of the jar. 



3. Cover the bottom of the jar with a 

 layer of cotton-wool and saturate it with 

 formalin. 



4. Remove the cotton- wool plug from 

 the culture tubes and place them, mouth 

 upward, inside the jar. (If water of con- 

 densation is present in any of the culture 

 tubes, it should be removed by means of 

 a capillary pipette before placing the tubes 

 in the formalin chamber.) 



5. Adjust the glass disc, ground side 

 downward, over the mouth of the jar and 

 secure it by pressing it firmly down into 

 the ointment, with a rotary movement. 



6. Remove the tubes from the formalin 



. FIG. 202. Bul- 



chamber after the lapse of a week, and loch's tubes, 

 dry the exterior of each. 



7. Seal the open mouth of each tube in the blowpipe 

 flame and label. 



If the cultivations are intended for museum purposes 

 when they are first planted, it is more convenient to 

 employ Bulloch 's tubes. These are slightly longer than 

 the ordinary tubes, and are provided with a constriction 

 some 2 cm. below the mouth (Fig. 202) a feature which 

 renders sealing in the blowpipe flame an easy matter. 



